Why does my volumetric light disappear when I disable camera visibility?
Disabling camera ray visibility prevents an object or shader from being evaluated until after a ray has bounced for the first time. Directly visible volumetric light comes from striking the volume on the first hit. By disabling camera ray visibility, you prevent this interaction since there is no first hit on the volume.

What exactly are you trying to accomplish? I'm not seeing anything wrong with your first image.

Btw, you may get somewhat improved performance by using an emission texture on your light itself instead of enclosing it in a sphere with holes. The texture will prevent sampling around the solid areas of the sphere. Use the texture coordinate > normal output to mapping on a point light.